The present inention relates to surface effect ships. The present invention relates more specifically to a surface effect ship including a catamaran type supported structure with two side hulls connected by a central box structure able to operate either as a displacement vehicle or as an air cushion lifted vehicle.
Many catamaran type ships have been suggested, with two side walls connected by a central box structure, particularly for the yatching. Such multi-hull boats are attractive especially from a safety point of view as, due to the lack of ballast and dead weight, they are virtually unsinkable. On the other hand, by comparison to the mono-hull, the multi-hulls are very fast due to the lack of ballast and they are less listing and rolling due to a larger righting momentum. The multi-hull ships provide also much larger deck areas.
Surface effect ships have also been suggested, including a catamaran type structure with two side hulls connected by a central box structure aboe to operate as air cushion supported vehicle. Such ships have been described in U.S. Pat. Nos. 3,977,491; 3,987,865; 4,090,459; and also in U.K. Pat. Nos. 1,210,973 and 1,242,131.
Generally these catamaran type surface effect ships include a lifted structure with a central box structure connecting two side hulls which provide the side confinement of the lifting air cushion; on the other hand, this structure is equipped with stern and bow seals able to assist the side hulls for delimiting the lifting air cushion supplied by the pressure air generator.
As described in French patent application No. 2,422,535, other designs have been considered as catamaran type surface effect ships able to operate either as displacement vehicles or as air cushion lifted vehicles. For these, the bow and stern sealing means are equipped with a seal lifting facility allow the ship to sail as a displacement ship.
Up to now, attempts to build such catamaran type surface effect ships, particularly ships with double operation modes, have concerned only low tonnage ships.
The suggested catamaran ship structure designs, allowing a large tonnage ship to bear correctly the longitudinal bending stresses, the transverse bending stresses, and the diagonal twist stresses, have a very large weight inconsistent with a surface effect ship operation.
Further, the turbine-compressor systems generating the air cushion used by the surface effect ships suggested until now have to be very powerful due to the significant weight of these ships.